Personal computers, mobile phones, video cameras, GPS devices and other information and telecommunication devices as well as endoscopes and other medical devices are becoming smaller with the advances in technology and, accordingly, electric wires used therein are always required to be made thinner and, for example, thin wires, such as AWG 40 and thinner wires, are currently required. For use in wiring in parts subject to bending in notebook-size personal computers and mobile phones, in particular, they are required to have performance characteristics enabling them to be used in severer environments.
With the reduction in electric wire thickness, electric wire coating/covering molding becomes difficult and, therefore, fluororesin coating materials are required to have improved moldability, and novel tasks are imposed on products after electric wire covering as well. The problems encountered on the occasion of electric wire covering molding, among others, are the roughness of the covering surface due to small protrusions appearing on the covering surface and the melt fracture occurring on the occasion of drawing the resin onto the conductor. These not only lower the yield in electric wire covering molding but also impair the quality of final products. As regards the products after electric wire covering, there are problems about crack resistance and about stripping properties of the covering which are required on the occasion of wiring. As the conducting wire becomes thinner, these problems become severer.
Concerning the prevention of melt fracture, a fluororesin which will not cause covering breakage when core wires with a diameter of 0.05 to 0.07 mm are coated under specific conditions has been proposed (cf. e.g. Patent Document 1).
Tetrafluoroethylene [TFE]- and perfluoro (alkyl vinyl ether) [PAVE]-based TFE copolymers containing 10 to 100 unstable terminal groups per 106 carbon atoms have been proposed as fluorocopolymers improved in crack resistance (cf. e.g. Patent Document 2 and Patent Document 3).
A TFE/PAVE copolymer showing a volume flow rate of 0.5 to 100 (mm3/second) (cf. e.g. Patent Document 4) and a TFE/PAVE copolymer showing a melt flow rate within the range of 35 to 60 g/10 minutes (cf. e.g. Patent Document 5) have been proposed as fluorocopolymers capable of giving moldings excellent in surface smoothness and crack resistance.
Patent Document 1: International Publication WO 2005/052015
Patent Document 2: Japanese Kokai Publication 2005-298659
Patent Document 3: Japanese Kokai Publication 2005-320497
Patent Document 4: Japanese Kokai Publication H08-109225
Patent Document 5: Japanese Kokai Publication 2002-53620